What are the risks and prevention measures for humans regarding toxoplasmosis in cats?

Toxoplasmosis in Cats: What Humans Need to Know

The primary risk of toxoplasmosis from cats comes from contact with soil or materials contaminated with cat feces containing infectious oocysts, not from direct contact with cats themselves. 1

Routes of Transmission and Risk Factors

Toxoplasma gondii is a parasite that can infect humans through several routes:

1. Cat-related transmission:

   • Cats are the only definitive hosts for T. gondii and the only animals that can shed infectious oocysts in their feces 1, 2
   • Oocysts become infectious 1-5 days after being shed 1
   • Cats typically shed oocysts only once in their lifetime, usually for just 3-10 days after their initial infection 3
   • Cats with antibodies to T. gondii have already completed shedding and no longer pose a risk 3

2. Other common transmission routes:

   • Ingestion of undercooked meat containing tissue cysts (especially pork, lamb, and venison) 1
   • Consumption of unwashed fruits/vegetables contaminated with soil containing oocysts 1
   • Drinking unpasteurized milk (especially goat milk) or contaminated water 1
   • Eating raw oysters, clams, or mussels 1

Health Risks

Toxoplasmosis poses particular risks to:

1. Pregnant women:

   • Infection during pregnancy, especially in the first trimester, can cause severe congenital infection 4
   • Most US women of childbearing age (91%) are susceptible to infection 1

2. Immunocompromised individuals:

   • HIV-infected persons, particularly those who are severely immunosuppressed, are at unusually high risk for developing relatively severe disease 1
   • Toxoplasmosis can cause severe disease affecting the central nervous system, muscles, lungs, and eyes 3

3. General population:

   • Most infections in immunocompetent individuals are asymptomatic or cause mild symptoms 4, 5
   • Toxoplasmosis is one of the most common pet-related parasitic infections in the United States 4

Prevention Measures

For Cat Owners:

1. Litter box management:

   • Change cat litter daily (T. gondii doesn't become infectious until 1-5 days after being shed) 1
   • Wear disposable gloves when cleaning the litter box 1
   • Wash hands thoroughly with soap and warm water after handling cat litter 1

2. Cat care practices:

   • Keep cats indoors to prevent hunting and consuming infected prey 1, 2
   • Feed cats commercial canned or dried food, not raw or undercooked meat 1
   • Control fleas in cats 1
   • Avoid adopting stray cats during pregnancy 1
   • Consider adopting cats older than 1 year (less likely to be shedding oocysts) 1

3. Personal hygiene:

   • Wash hands after contact with cats 1
   • Don't allow cats to lick open wounds 1
   • Avoid rough play with cats that might lead to scratches 1

For Everyone:

1. Food safety:

   • Cook meat thoroughly to proper temperatures:
     • 63°C (145°F) for whole cuts (excluding poultry)
     • 71°C (160°F) for ground meat (excluding poultry)
     • 74°C (165°F) for all poultry 1
   • Freeze meat at -20°C (-4°F) for at least 48 hours to kill tissue cysts 1
   • Wash hands, kitchen surfaces, and utensils after handling raw meat 1
   • Avoid consuming unpasteurized milk, especially goat milk 1
   • Avoid raw oysters, clams, and mussels 1

2. Gardening and outdoor activities:

   • Wear gloves when gardening or handling soil 1
   • Wash hands thoroughly after gardening or contact with soil 1
   • Wash all fruits and vegetables thoroughly 1

Common Misconceptions

1. Direct contact with cats is not the primary risk:

   • The risk comes from contact with infectious oocysts in cat feces, not from petting or handling cats 2, 5
   • Due to cats' fastidious nature, oocysts are rarely found on their fur 2

2. Indoor cats pose minimal risk:

   • Cats that don't hunt or consume raw meat are unlikely to become infected 2
   • Cats that have already been infected and developed antibodies no longer shed oocysts 3

3. Knowledge gaps among pregnant women:

   • While 61% of pregnant women in one study knew that T. gondii is shed in cat feces, only 30% were aware it can be found in raw/undercooked meat 6
   • Many pregnant women practice good preventive behaviors despite limited knowledge 6

Special Considerations for High-Risk Groups

Pregnant Women:

• Follow all prevention measures listed above
• Consider delaying acquisition of new cats during pregnancy 1
• If already owning a cat, have someone else clean the litter box if possible 1

Immunocompromised Individuals:

• Should carefully consider the risks of cat ownership 1
• If acquiring a cat, choose one older than 1 year and in good health 1
• Discuss risks with healthcare providers 1

By following these preventive measures, the risk of toxoplasmosis transmission from cats can be significantly reduced while still enjoying the benefits of cat companionship.